The present invention pertains to microphones, and more particularly to a microphone associated with a vehicle accessory such as a rearview mirror assembly or the housing of a rear vision display device.
It has long been desired to provide improved microphone performance in devices such as communication devices and voice recognition devices that operate under a variety of different ambient noise conditions. Communication devices supporting hands-free operation permit the user to communicate through a microphone of a device that is not held by the user. Because of the distance between the user and the microphone, these microphones often detect undesirable noise in addition to the user's speech. The noise is difficult to attenuate. A particularly challenging hands-free application where dynamically varying ambient noise is present is a hands-free communication system for a vehicle. For example, bi-directional communication systems such as two-way radios, cellular telephones, satellite phones, and the like, are used in vehicles, such as automobiles, trains, airplanes and boats. For a variety of reasons, it is preferable for the communication devices of these systems to operate hands-free, such that the user need not hold the device while talking, even in the presence of high ambient noise levels subject to wide dynamic fluctuations.
Bi-directional communication systems include an audio speaker and a microphone. In order to improve hands-free performance in a vehicle communication system, a microphone is typically mounted near the driver's head. For example, a microphone is commonly attached to the vehicle visor or headliner using a fastener such as a clip, adhesive, hook and loop fastening tape (such as VELCRO® brand fastener), or the like. The audio speaker associated with the communication system is preferably positioned remote from the microphone to assist in minimizing feedback from the audio speaker to the microphone. It is common, for example, for the audio speaker to be located in a vehicle adaptor, such as a hang-up cup or a cigarette lighter plug used to provide energizing power from the vehicle electrical system to the communication device. Thus, although the communication system designer knows the position of the audio speaker in advance, the position of the microphone is unknown as the user can position the microphone where they choose. The position of the microphone relative to the person speaking will determine the level of the speech signal output by the microphone and may affect the signal-to-noise ratio. The position of the microphone relative to the audio speaker will impact on feedback between the speaker and microphone. Accordingly, the performance of the audio system is subject to the user's installation of the microphone. Additionally, the microphone will typically include a wire, which if it is mounted to the surface of the vehicle interior, will not be aesthetically pleasing. Alternatively, if the wire is to be mounted behind the interior lining, the vehicle interior must be disassembled and then reattached so that the wire can be hidden, which may result in parts that rattle loudly or hang loosely from the vehicle frame.
One potential solution to avoid these difficulties is disclosed in U.S. Pat. No. 4,930,742, entitled “REARVIEW MIRROR AND ACCESSORY MOUNT FOR VEHICLES”, issued to Schofield et al. on Jun. 5, 1990, which uses a microphone in a mirror mounting support. Although locating the microphone in the mirror support provides the system designer with a microphone location that is known in advance, and avoids the problems associated with mounting the microphone after the vehicle is manufactured, there are a number of disadvantages to such an arrangement. Because the mirror is positioned between the microphone and the person speaking into the microphone, a direct unobstructed path from the user to the microphone is precluded. Additionally, the location of the microphone on the windshield detrimentally impacts on microphone design flexibility and overall noise performance of the microphone.
U.S. Pat. Nos. 5,940,503, 6,026,162, 5,566,224, 5,878,353, and D 402,905 disclose rearview mirror assemblies with a microphone mounted in the bezel of the mirror. None of these patents, however, discloses the use of acoustic ports facing multiple directions nor do they disclose microphone assemblies utilizing more than one microphone transducer. The disclosed microphone assemblies do not incorporate sufficient noise suppression components to provide output signals with relatively high signal-to-noise ratios, and do not provide a microphone having a directional sensitivity pattern or a main lobe directed forward of the housing and attenuating signals originating from the sides of the housing.
It is highly desirable to provide voice recognition systems in association with vehicle communication systems, and most preferably, such a system would enable hands-free operation. Hands-free operation of a device used in a voice recognition system is a particularly challenging application for microphones, as the accuracy of a voice recognition system is dependent upon the quality of the electrical signal representing the user's speech. Conventional hands-free microphones are not able to provide the consistency and predictability of microphone performance needed for such an application in a controlled environment such as an office, let alone in an uncontrolled environment such as an automobile.
Accordingly, there is a need for a microphone for a vehicle providing improved hands-free performance and preferably enabling voice recognition operation.
Historically, automotive microphones have utilized a two wire interface to provide an audio signal from the microphone assembly to an electronic assembly (e.g., an amplifier stage). This two wire interface has also provided a power source to the microphone assembly and a wetting current through the interface such that reliable continuity was maintained between the microphone and the electronic assembly (see FIG. 35 and the description below).
Digital signal processors (DSPs) or other more advanced circuitry that may be used within a microphone assembly require more power than can normally be delivered through a standard two wire interface. As such, microphone assemblies incorporating DSPs may also require an auxiliary power source to be incorporated within the microphone assembly. However, implementing an auxiliary power source within a microphone assembly can introduce ground loops. Further, when non-precious metal contacts are used in a connector of a microphone interface, the contacts of the interface are prone to oxidation, which eventually leads to a continuity problem between the microphone assembly and the electronic assembly.
Thus, what is needed is a microphone interface for automotive microphone assemblies that include a power source that provides reliable continuity.